As is well known in the art, modern automotive vehicle engines are produced with circulating oil lubrication systems wherein oil is forced under pressure by means of the engine driven oil pump from the oil sump or pan through various lubricating passages to the critical points of lubrication of the engines. In order to remove or at least minimize oil contaminants within such engine lubrication systems, it has been the practice to incorporate oil filters therein. It is usually the case that such filters are of the replaceable type and as such, the filter units are periodically discarded and replaced, usually concurrently with the replacement of the engine lubricating oils. Generally, oil filters produced and sold for both original equipment and replacement on automotive vehicles operate on the same principle; namely, the filter units are provided with a filtering media or element and under normal operating conditions, oil enters at the top of the filter through a series of holes leading to the outer periphery of the filtering media. The oil then passes through the filtering media during which the oil contaminants are removed and the oil thereafter passes centrally through the filter element and exits through an outlet port, from where the oil is communicated back through the lubrication system of the vehicle engine. Frequently, anti-drainback valves are used which prevent the oil from draining out of the filter after the engine has stopped operating, and in many instances, the filter units are provided with pressure relief valves which provide means for bypassing the filter element or media at such time as a predetermined pressure drop occurs across the filter element, i.e., when the lubricant is in a highly viscous state such as during low temperature operating conditions.
In order for the lubrication systems of the aforementioned type of engines to operate satisfactorily, the lubricant or oil must have certain properties that insure both adequate system flow and minimum performance after delivery. At the same time, the oil must not have any tendency to degrade the life or performance of any component parts of the vehicle engine with which it comes into contact. In light of these requirements, several categorical properties and their acceptable performance levels have been established. Such properties and performance levels include oil viscosity, oil oxidation rate, anti-wear properties, detergent and dispersant properties, and anticorrosion properties. More particularly, engine oil used in modern automotive, as well as light truck, engines are specified by two separate classifications. The first is the engine service classification and relates primarily to the performance of the engine oil under simulated service operating conditions. Typical requirements are a maximum increase in viscosity which would indicate the presence of contaminants in the engine after certain sequential operations, the presence of scuffing and actual wear of certain parts of the oil testing apparatus (typically a specified type of engine), and the presence of other deposits, such as varnish and the like on engine piston rings. The second classification is based on the viscosity of the oil at 0.degree. F. and at 210.degree. F., and engine oils are normally rated at either the 0.degree. F. point, the 210.degree. F. point or at both. For example, a typical specification would be 10W indicating a performance level only at 0.degree. F.; 30 indicating a performance level only at 210.degree. F. or 10W30 indicating minimum performance levels at both 0.degree. F. and 210.degree. F.
Producers of engine oils have found that in order to meet the aforesaid service classifications, petroleum oils by themselves are unsuitable. Consequently, a typical engine lubricating oil contains between 10% and 20% additives or non-oil components, in order to meet these classification requirements. Typical components needed to meet the service classification are detergents, dispersants, inhibitors, anti-wear agents and anti-corrosive agents. Those lubricants of the multiple viscosity or multi-grade type require an additive or component in them to provide for acceptable performance at the requisite viscosity levels. Such additives or components are known in the art as viscosity improvers or viscosity index (VI) improvers. Unfortunately, however, many of the additive components of modern engine oils degrade with use, either because of (a) inherent deficiencies, or (b) because their function is, in fact, to be consumed or depleted to provide the necessary or desired feature in the lubricant. More particularly, oil viscosity improvers fall into category (a) since they consist of very large molecules which break up during use so that they can no longer perform their intended function. This breaking up of the VI molecules is referred to as shear-instability, which results from the fact that the molecules are unstable when subjected to high fluid shear rates. In the second category (b) are those types of oil additives which are sacrificed or which are purposely consumed during the service life of the oil. Examples of such sacrificial additives are anti-oxidants which function to prevent the deterioration associated with oxygen attack on the lubricant base fluid. Normally, anti-oxidants are provided in the oil for the purpose of absorbing any oxygen present and thus, among other things, such additives prolong the resistance of the oil to form sludge. Over the service life of the oil, however, the anti-oxidant additives become saturated and hence the resistance of the oil to form sludge gradually terminates. Anti-wear and anti-corrosive additives or compounds are similar to anti-oxidants in that these additives are intended to be deposited on the engine surfaces. Because of the washing action of the oil and the rubbing of the metal surfaces during operation of the engine, however, such deposits do not remain on the critical surfaces and must be replenished at these points from the lubricant. When the concentration of these additives drops below a certain level, the additives can no longer be depositive and hence the engine components are subject to wear and corrosion.
In view of the finite life of the lubricant additives which are utilized in modern engine oils, either because of the inherent deficiencies of such additives or because of their depletion (sacrificial) characteristics, it has heretofore been proposed to replace or replenish such additives and thereby extend the service life of the engine oils. The prior art is replete with a myriad of different ways of effecting such replacement of engine oil additives, and among such prior art teachings are those methods disclosed in the below discussed United States patents which, while being related to the subject matter of the invention disclosed herein, are not believed to be anticipatory of the applicant's inventive concepts as defined in the claims appended hereto.
U.S. Pat. No. 2,302,552, for Method and Apparatus for Treating Lubricant Oils, discloses a way of replenishing lubricating oil additives by impregnating an absorbant material, such as the filter material, with a sparingly soluble additive compound such that the passage of lubricating oil through the filter media effects a progressive dissolution of the additives therein. The absorbant material itself is insoluble in the oil.
U.S. Pat. No. 2,310,305, for Method and Means for Purifying Lubricants, discloses a system for effecting a continuous replenishment of additive agents in a recirculating engine oil system by providing a separate reservoir or chamber, and preferably utilizing the oil filter itself for incorporating additive agents of low solubility which are contacted by the oil passing through the reservoir or filter to effect a progressive dissolving thereof. It is suggested in this patent that fine particles can be loaded within the filter cartridge or the material of which the filter cartridge is comprised can be coated with the additive substance. Alternatively, or in conjunction with the foregoing, a solid or semi-solid or porous mass of the material or of an inhibitor impregnated inert material may be positioned within the filter chamber so as to be continuously contacted by the oil passing therethrough.
U.S. Pat. No. 2,435,707, for Method and Apparatus for Treating Oil, discloses a system for maintaining the effectiveness of the detergent additives present in engine lubricating oils by continuously adding to the lubricant oil an amino soap additive which is very slightly soluble in the oil so as to cause an agglomeration of the detergent suspended colloidal dirt particles in the oil in order that they attain a size in which they can be removed by the filter.
U.S. Pat. No. 2,898,902, for Apparatus for Supplying Additives to Lubricating Systems, discloses a mechanical metering system for effecting a periodic replenishment of the additives. The metering system is actuated on a time basis or other cycle, such as, for example, each time the engine is started, whereby a metered quantity of an additive or blend of additives is injected into the crankcase of the vehicle engine.
U.S. Pat. No. 2,943,737, for Filter and Method of Purifying Oil, discloses an oil filter in which the filter medium is coated with a thermoplastic resin selected from the group consisting of polyethylene glycol and polypropylene glycol. While the obstensible purpose of the coating is to improve filtering efficiency, apparently some of the polyglycol resin does dissolve and evidently does have a detergent boosting affect.
U.S. Pat. No. 3,314,884, for Fuels and Lubricants Containing Inclusion Compounds. This patent discloses a technique for supplying active chemical additives to a lubricating oil composition. A release of the additive is achieved by any mechanism which destroys a framework of a surrounding inclusion or housed compound and such techniques include melting, dissolving or other disintegrating of the structure of the housed compound.
U.S. Pat. No. 3,749,247, for Addition of Oxidation Inhibitor to Lubricating Oil, discloses a system for replenishing the additives in crankcase motor oils, and in particular, anti-oxidants in the oil, by placing plastic containers composed of polyolefin materials which are filled with liquid additive compounds and are positioned within gaps between the filter element flutes. The additive compound passes through the walls of the container by diffusion at a rate consistent with the need for replacing the anti-oxidant additive in the oil.
All of the various concepts disclosed in the aforementioned patents, while generally addressing themselves to the problems resulting from oil additive depletion, are subject to various objectionable criticisms, due primarily to the complexity of the systems and methods proposed therein and the resultant difficulties of adapting such proposed systems in commercially acceptable filter units. Additionally, such proposed systems are seen to be objectionable from the standpoint that there is no single system or method proposed therein which provides for the replenishment of the three most important oil additives which become depleted throughout the service of the oil, namely, the viscosity index improvers, anti-oxidants, and anti-wear-anti-corrosion compounds. Moreover, such heretofore proposed systems suffer the extremely important shortcoming of not assuring against over or underdosing of the additives, a characteristic which can be as detrimental to the engine oil and engine component parts as the depletion of the original oil additives. For example, if the engine oil is provided with an overdose of a VI improver, there is a marked reduction in the low temperature performance of the oil which in turn results in engine starting difficulties at low operating temperatures.
U.S. Pat. No. 3,336,223, for Method and Means For Maintaining An Effective Concentration of Additives in Oil, discloses a system for prolonging the useful life of lubricating oils and is believed to disclose a system which overcomes many of the objectionable characteristics of the various systems described in the aforementioned patents. In particular, the system set forth in the '223 patent contemplates providing a oil soluble solid thermoplastic polymer within an oil filter enclosure and impinging the polymer with the circulating oil, whereby oil additives which are compounded into the polymer will be gradually dispersed into the oil. In spite of the many advantages that the system disclosed in the U.S. Pat. No. 3,336,223 patent has over the prior art, this patent falls short at least in one important respect of teaching an additive replenishing system that provides for the optimum rate of additive replenishment during the service life of the oil, and this particular shortcoming has been found to be extremely critical in assuring optimum effective oil life. In particular, it has been found that optimum oil life is achieved in those cases wherein the oil additives are replenished at a relatively uniform or linear rate so as to thereby replenish the original oil additives at essentially the same rate as they become depleted, thus positively assuring against over or underdosing of the additives. In accordance with the present invention, it has been discovered that in order to provide for a linear or constant rate of additive replenishment, it is imperative that the polymer body having the oil additives compounded therein be located at an area within the associated filter enclosure wherein a minimum amount of oil circulation occurs, i.e., a relatively stagnant oil circulating area. By so locating the polymer-additive compound, consistently uniform and linear dispersion or dissolution of the polymer compound will occur, thereby assuring for a linear replenishment of the additives over the desired service life (i.e., between drain intervals) of the engine oil, as will be hereinafter described in detail.